Modeling the Polymorphism of Pentacene

Abstract

Thin films of pentacene are known to crystallize in at least four different polymorphs. All polymorphs are layered structures that are characterized by their interlayer spacing d(001). We develop a model that rationalizes the size of the interlayer spacing in terms of intralayer shifts of the pentacene molecules along their long molecular axes. It explains the wide variety of interlayer spacings, without distorting the herringbone pattern that is characteristic of many acenes. Using two simple theoretical models, we attempt to relate the intralayer shifts with the dominant, although weak, interatomic interactions (van der Waals, weak electrostatic, and covalent). For two polymorphs, a consistent picture is found. A full understanding of the other two, substrate-induced, polymorphs probably requires consideration of interlayer interactions.

Arrays of crystalline C60 and pentacene nanocolumns

“…For pentacene on oxidized Si, we find two series of peaks denoted with squares and circles, which can be assigned to the 00l series of the pentacene thin film phase ͑squares, measured lattice spacing of d 001 = 1.541 nm͒ and of a recently reported pentacene bulk phase ͑circles, d 001 = 1.437 nm͒, respectively. 21,22 This preferred orientation of pentacene on oxidized Si is well documented in the literatures. Additionally, less intense peaks can be assigned to crystal planes of another different pentacene polymorph 23 ͓marked with the respective indices ͑hkl͒ in Fig.…”

Symmetry Dependence of Vibration-Assisted Tunneling

“…This regime is highly relevant, resembling electron hopping in organic and molecular electronics. Note that vibronic spectroscopy is very different from usual STMbased inelastic electron tunneling spectroscopy [8], for which it has been realized that the symmetries of wave functions play an important role [9][10][11].As a model system we chose pentacene, which is widely used in organic electronics and one of the best studied systems [4,5,12,13]. We consider only transport involving the first molecular resonances, attributed to occupation and depletion of the lowest unoccupied molecular orbital (LUMO) and highest occupied molecular orbital (HOMO) level, respectively.…”

“…As a model system we chose pentacene, which is widely used in organic electronics and one of the best studied systems [4,5,12,13]. We consider only transport involving the first molecular resonances, attributed to occupation and depletion of the lowest unoccupied molecular orbital (LUMO) and highest occupied molecular orbital (HOMO) level, respectively.…”

A Polymorph Lost and Found: The High‐Temperature Crystal Structure of Pentacene

“…[9,11] In all of these phases, pentacene molecules align their long axis approximately perpendicular to the film surface, and are thought to adopt a herringbone-type arrangement in the resulting twodimensional layers. [9,12,13] Several different d-spacings perpendicular to the thin-film surface have been observed, with values of 14.1, 14.5, 15.0, and 15.5 Å, [11,13] sometimes used to label the different polymorphs. The relative concentration of these phases appears to be strongly dependent upon the deposition conditions.…”